
SiBE061121_A
Function of Thermistor
Function and Control
39
2. Function of Thermistor
(1) Outdoor Heat
Exchanger
Thermistor
1. The outdoor heat exchanger thermistor is used for controlling the target discharge pipe
temperature. The system sets the target discharge pipe temperature according to the
outdoor and indoor heat exchanger temperature, and controls the outdoor electronic
expansion valve opening so that the target discharge pipe temperature can be obtained.
2. In cooling operation, the outdoor heat exchanger thermistor is used for detecting the
disconnection of the discharge pipe thermistor. When the discharge pipe temperature drops
below the outdoor heat exchanger temperature by more than a certain value, the discharge
pipe thermistor is judged as disconnected.
3. In cooling operation, the outdoor heat exchanger thermistor is used for high pressure
protection.
(2) Discharge
Pipe Thermistor
1. The discharge pipe thermistor is used for controlling discharge pipe temperature. If the
discharge pipe temperature (used in place of the inner temperature of the compressor) rises
abnormally, the operating frequency becomes lower or the operation halts.
2. The discharge pipe thermistor is used for detecting disconnection of the discharge pipe
thermistor.
(3) Indoor Heat
Exchanger
Thermistor
1. The indoor heat exchanger thermistor is used for controlling the target discharge pipe
temperature. The system sets the target discharge pipe temperature according to the
outdoor and indoor heat exchanger temperature, and controls the outdoor electronic
expansion valve opening so that the target discharge pipe temperature can be obtained.
2. In cooling operation, the indoor heat exchanger thermistor is used for freeze-up protection
control. If the indoor heat exchanger temperature drops abnormally, the operating frequency
becomes lower or the operation halts.
3. In heating operation, the indoor heat exchanger thermistor is used for detecting the
disconnection of the discharge pipe thermistor. When the discharge pipe temperature drops
below the indoor heat exchanger temperature by more than a certain value, the discharge
pipe thermistor is judged as disconnected.
(4) Radiant
Panel
Thermistors
1. The radiant panel thermistors are used for calculating radiant panel surface temperature. Due to
structural and manufactural restrictions, the radiant panel surface temperature cannot be
controlled directly with a thermistor. Thermistors are mounted on the radiant panel piping in order
to calculate the radiant panel surface temperature.
The indoor electronic expansion valve is controlled according to the radiant panel surface
temperature.
2. The radiant panel thermistors are used for detecting malfunction of the indoor electronic
expansion valve.
Compressor
(2)
(4)
φ
4
(4)
φ
6
Outdoor electronic
expansion valve
Indoor electronic
expansion valve
(Motor operated
valve)
Radiant panel
Four way valve
(R14640)
(1)
(3)